How do I calculate density?

Divide mass by volume. A 200 gram object occupying 50 cubic centimetres has a density of 4 g/cm³, or 4,000 kg/m³ — the units matter, but the arithmetic does not change.

Why does a steel ship float?

Because what matters is the average density of the whole vessel, not of the steel. The hull encloses a great deal of air, bringing the average well below water's 1,000 kg/m³.

What is the density of water?

1,000 kg/m³ at 4°C, equal to 1 g/cm³ and 1 kg per litre. The metric system was designed around that relationship, which is why the numbers are so clean.

Because water is unusual: it is densest at 4°C and expands as it freezes, so ice is about 8 percent less dense than liquid water. Almost every other substance is denser as a solid.

Does density change with temperature?

Yes. Most substances expand when heated and become less dense, which is what drives convection. Water reverses this below 4°C, which is why lakes freeze from the top down.

Density Calculator

Solve ρ = m/V for density, mass or volume, with common materials for comparison.

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About the Density Calculator

Density is mass divided by volume, and it is what determines whether something floats. An object floats in a fluid less dense than itself — which is why a steel ship floats: the hull encloses air, so the average density of the whole vessel is far below that of water.

Water at 4°C is 1,000 kg/m³, which is the reference the metric system was built around: one gram per cubic centimetre, one kilogram per litre. That is not a coincidence but a definition, and it makes water a convenient benchmark for everything else.

Density changes with temperature, and water is famously anomalous. It is densest at 4°C and expands as it freezes, which is why ice floats and why pipes burst. Almost every other substance is densest as a solid.

How it works

Choose density, mass or volume as the unknown.
Enter the other two — kilograms and cubic metres, or grams and cubic centimetres, since the ratio is the same.
Compare the result against common materials listed below.

Frequently asked questions

How do I calculate density?: Divide mass by volume. A 200 gram object occupying 50 cubic centimetres has a density of 4 g/cm³, or 4,000 kg/m³ — the units matter, but the arithmetic does not change.
Why does a steel ship float?: Because what matters is the average density of the whole vessel, not of the steel. The hull encloses a great deal of air, bringing the average well below water's 1,000 kg/m³.
What is the density of water?: 1,000 kg/m³ at 4°C, equal to 1 g/cm³ and 1 kg per litre. The metric system was designed around that relationship, which is why the numbers are so clean.
Why does ice float?: Because water is unusual: it is densest at 4°C and expands as it freezes, so ice is about 8 percent less dense than liquid water. Almost every other substance is denser as a solid.
Does density change with temperature?: Yes. Most substances expand when heated and become less dense, which is what drives convection. Water reverses this below 4°C, which is why lakes freeze from the top down.

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